The objectives of the proposed research are to isolate and characterize--physico-chemically and immunologically--cholera related heat-labile enterotoxins (LT) from E. coli strains which produce diarrheal disease in man and animals. In recent previous work, we have isolated, for the first time, E. coli LT from a K-12 strain infected with a tox plasmid of porcine origin. The homogeneous enterotoxin was similar, but not identical, to choleragen (the cholera enterotoxin) structurally and immunologically. Partial amino acid sequence determination revealed that 15 of the first 20 N-terminal amino acids were identical in both toxins. The toxin had been purified by exploiting its unique affinity for agarose containing gels. These observations will be extended with additional strains of E. coli of human and animal origins. The immunologic and structural relationships of these toxins will be compared.